Copepod cryptic species as aquatic invaders

Abstract. The dispersal of aquatic organisms has especially increased since the 19th century, mainly due to the introduction of metal ships with ballast compartments or with birds. Along with easily visible aquatic organisms, there are invasions of less noticeable aquatic organisms, like copepods, which can mainly be recognized by experts. A special group is made up of cryptic species for which morphological identification is inaccessible or very difficult. This review is devoted to the identification, description and analysis of the dispersal routes of three copepod cryptic species complexes into waterbodies. Using molecular-genetic methods, Eurytemora carolleeae introduction were revealed in 2007. After describing this invader as a new species, its distribution was also studied using morphology. The invasions of Acanthocyclops americanus and Eurytemora caspica were mainly studied using morphological methods since the species have already been described; however, molecular-genetic methods were also used to confirm their distinctions from local forms. The real distribution of the former cosmopolitan species Eucyclops serrulatus was studied using a multidisciplinary approach that combined molecular-genetic, cross-hybridization and morphological methods. Judging by the distribution of local E. serrulatus sensu stricto populations in coastal waterbodies of most continents, this species can apparently serve as a good marker of the species dispersal processes with ships. The three possible scenarios resulting from cryptic species introductions and their interaction with local fauna were competitive displacement (A. americanus), competitive coexistence (E. carrolleeae) and independent development without competition (E. serrulatus). The role of cryptic species invasion in aquatic biodiversity modification is discussed.